1. Field of the Art
This invention relates to a flexible sheathing tube construction particularly suitable for use on insertion type examination instruments having a flexible elongated component part fitted in a flexible sheathing tube as in the case of flexible insertion rods of endoscopes and ultrasound probes which are designed to be introduced into internal cavities in humane bodies or machines or other internal spaces, and a method for fabrication of such flexible sheathing tube.
2. Prior Art
For instance, an endoscope, which is typical of instruments designed to be introduced into internal cavities or spaces in human bodies or machines for examination purposes, is largely constituted by a manipulating head assembly providing manipulating control means for the endoscope, an elongated flexible insertion rod containing a component part or parts for carrying out examinations in intracavitary portions of human body and extended forwardly from the manipulating head assembly, and a flexible universal cable extended rearward from the manipulating head assembly to connect the endoscope detachably to an illumination light source or to a signal processing unit in case of an electronic endoscope. Except for a proximal end portion which is connected to the manipulating head assembly and a short rigid tip end section which accommodates endoscopic observation means at the distal end of the endoscope, the endoscopic insertion rod is constituted by a tubular flexible rod section almost over its entire length, the flexible rod section being capable of flexibly bending its body into conformity with the shape of a path of insertion. Normally, the flexible rod section is connected to the rigid tip end section through an angle section which can be manipulated through an angle knob provided on the manipulating head assembly to turn the rigid tip end section into a desired direction.
In order to illuminate dark intracavitary portions under endoscopic observation, the rigid tip end section is normally provided with an illumination window in addition to an observation window, permitting the operator to observe intracavitary regions of particular interest under illuminated conditions. Accordingly, it is essential for an endoscopic observation means to have an illumination system in combination with an endoscopic observation system.
Typically, an endoscopic illumination system is constituted by a light guide in the form of a bundle of extra fine fiber optics, and an illumination window located in front of a light emitting end of the light guide to disperse illumination light rays over a predetermined range within an intracavitary region. The light guide is extended through the entire length of the insertion rod and down to the proximal end of the universal cable via the manipulating head assembly.
On the other hand, an endoscopic observation system includes an objective lens which is fitted in the observation window, and an image pickup means which is located at the focus of the objective lens, i.e., an electronic image sensor like a CCD or a light entrance end of an optical image guide in the form of a fiber optics bundle or the like. In case of an electronic endoscope, a signal cable from a CCD is also passed through the flexible insertion rod and the universal cable via the manipulating head assembly together with the afore-mentioned illumination light guide. In case of an optical endoscope, an image guide is passed through the flexible insertion rod up to an eyepiece which is connected to the housing of the manipulating head assembly of the endoscope.
In addition to the above-described endoscopic illumination and observation systems which are minimum essentials, endoscopes are generally provided with means for bioptic or therapeutic treatments such as sampling of cells, extraction of diseased portions, stanching etc. In order to permit insertion of forceps, high frequency surgical instruments or other instruments which are necessary for these treatments, endoscopes are provided with the so-called biopsy channel extending from the manipulating head assembly down to the distal end of the flexible insertion rod. Besides, it is often the case that the endoscopic insertion rod includes a cleansing means for cleaning the observation window which is susceptible to contaminations with body fluids. An observation window cleansing means of this sort usually includes an air/water feed nozzle which is located and opened in the proximity of the observation window at the distal end of the insertion rod. The air/water feed nozzle is connected to an air/water feed tube which is placed in the rigid tip end section and the angle section of the endoscopic insertion rod. In the flexible rod section, the air/water tube is bifurcated into an air feed tube and a water feed tube which are extended all through the flexible rod section up to air and water supply ports on the manipulating head assembly of the endoscope.
Accordingly, the flexible rod section of the endoscopic insertion rod needs to receive therein the abovedescribed light guide, signal cable (or image guide) which are extended to or from the endoscopic observation means on the rigid tip end section, and in some cases need to further receive the biopsy channel, air feed tube and water feed tube as mentioned above. As explained hereinbefore, the flexible rod section should be capable of bending its body in arbitrary directions in conformity with the shapes of various bends in a path of insertion. Therefore, the light guide or other elongated members to be fitted in the flexible rod section need to be formed of a flexible or pliable material.
Further, the flexible rod section which contains fragile component part like a light guide is required to have satisfactory properties in shape retainability and anti-crushing strength, together with unresisting bending flexibility for advancement along a path of insertion which could take various shapes. In other words, despite the requirement for easily bending pliability, the flexible rod section is at the same time required to have a structure which is rigid enough for transmitting a propelling thrust securely to the rigid tip end section at the time of insertion into an intracorporeal portion to be examined.
In order to satisfy these requirements, the flexible rod section of an endoscope is usually composed of a flexible tubular base structure in the form of an open helical coil structure which is formed by winding a narrow thin resilient metal strip helically into a cylindrical shape in a predetermined open pitch, a protective mesh sleeve of wire netting which is fitted on the helical substructure, and an outer skin layer of a resilient synthetic resin material laminated to cover the protective net. Usually, the flexible base structure of the sheathing tube has a double coil construction consisting of inner and outer open helical coil members of opposite winding directions. The protective mesh sleeve is impregnated with an adhesive and thereby securely bonded to the respective open helical coil members of the flexible base structure. The flexible sheathing tube, which is composed of, from the inner side, a flexible base structure of the double coil construction, a protective mesh sleeve and an outer skin layer in the above-described manner, can perform the functions of flexibly bending an insertion rod in desired directions and retaining the shape of the rod, particularly, the shape of the internal space of the insertion rod against deformations.
However, in addition to the above-described requirements, the flexible sheathing tube of the endoscopic insertion rod has to meet other requirements, for example, smooth operationability at the time of insertion into the body of a patient and reductions in diameter for lessening pains on the part of patient. In this regard, if one tries to reduce the diameter of the flexible sheathing tube while maintaining its shape retainability and anti-crushing strength, there will arises a problem of frictional contact of internally fitted endoscopic component parts such as the light guide and biopsy channel, with each other or with inner surfaces of the flexible sheathing tube itself. Accordingly, it becomes necessary to provide measures for protecting these internally fitted components against damages which might result from such frictional contact, particularly, from frictional contact with the helical metal coil members on the innermost position of the flexible sheathing tube. This is because, even if the metal strips of the open helical coil members were rounded off beforehand at the respective lateral side edges, they would still have possibilities of damaging or breaking a fragile component part like the light guide easily when forced into frictional sliding contact with each other. Besides, considering the use of a high frequency surgical instrument through the biopsy channel, preferably any metal member should not be allowed to remain in an exposed state on the inner side of the flexible sheathing tube.
Further, since the inner and outer metal coil members of the above-mentioned flexible base structure of the sheathing tube are in the form of open helical coils each having the respective helices spaced from each other by a gap space of a predetermined width and placed in position in an overlapped state in surface contact with helices of other coil member, it is very likely for the inner and outer helical coil members to be subjected to a twisting force in different degrees and in different directions when a bending force is exerted on the insertion rod, resulting in relative sliding contact of the two helical coil members and in irregular spacings between the individual helices of the respective coil members. As soon as the insertion rod is stretched again into a rectilinear form, normally such irregularly spaced helices restore original regularly spaced conditions by resiliency of the coils. However, if the flexible insertion rod section is bent repeatedly to exert deformative forces on the flexible sheathing tube at a relatively high frequency, the individual helices of the inner and outer coil members tend to remain in irregularly spaced positions, giving rise to irregularities in rigidity in the axial direction of the endoscopic insertion rod.
From a standpoint of higher adaptability of the insertion rod to a path of insertion, the sheathing tube is preferred to have as high flexibility as possible. However, the higher the flexibility of the sheathing tube, the lower becomes the strength in stretching and contracting directions of the insertion rod. Accordingly, at the time of insertion of the flexible insertion rod, there might occur a situation in which a fore end portion of the flexible sheathing tube is compressed too easily, narrowing the spacings between the helices in that portion to such a degree as to lower the flexibility of the insertion rod conspicuously in bending directions. Besides, application of a compressive force on the flexible sheathing tube could cause detachment of the protective mesh sleeve off the outer helical coil member, which in turn could lead to a detrimental damage to the outer skin layer of the sheathing tube. Namely, a flexible sheathing tube which has an outer and inner helical coil members simply superposed one on the other cannot be considered to be sufficient in durability and reliability.
Particularly, an axial fore end portion of the endoscopic insertion rod is required to have a high degree of flexibility to ensure its easy bending motions along a path of insertion. On the other hand, on the side of the proximal end, the insertion rod is required to have a certain degree of rigidity to improve transmission of a propelling force or thrust through the rod being advanced toward an intracavitary portion of interest. As for means for controlling the rigidity in the axial direction of the flexible sheathing tube, attempts have been made to vary the width of metal strips for the helical coil members or of gap spaces between the respective helices of the coil members which are wound in an open pitch, to vary the mesh size of the protective mesh sleeve, or to vary the amount of application of an adhesive in the axial direction of the sheathing tube. Since all of these means have inherent problems, there have been strong demands for improved means which can vary the rigidity in the axial direction of the flexible sheathing tube in a stable and reliable manner.